The present invention relates to a planar display device such as an organic electroluminescence (EL) display device, and a method of manufacturing the same. In particular, this invention relates to an active matrix type planar display device and a method of manufacturing the same.
There has been an increasing demand for planar display devices, represented by liquid crystal displays, which are thinner, lighter and less in power consumption than CRT display devices. In particular, active matrix type planar display devices, wherein each display element is provided with a switching device, have been applied to various displays of mobile information apparatuses, etc. The active matrix planar display device has a high display quality, with no crosstalk between adjacent display elements.
Recently, organic electroluminescence (EL) display devices have been widely developed as self-luminescence type displays, which realize higher response speeds and wider angles of view field. The organic EL display device comprises an organic EL panel and an external drive circuit for driving the organic EL panel. The organic EL panel comprises a display region in which display elements are arranged in a matrix on a support substrate of glass, etc., and a drive circuit region for driving the display elements by signals from the external drive circuit. Each display element comprises a first electrode, a second electrode disposed to oppose the first electrode, and an organic light-emission layer disposed between the first and second electrodes.
In the organic EL display device, EL light is let out by a back-face luminescence method in which light is emitted via the support substrate, or a top-face luminescence method in which light is emitted from the side opposing the support substrate. In the active matrix type organic EL display device adopting the back-face luminescence method, circuits of thin film transistors (TFTs), which block transmission of EL light, are disposed under the organic light-emission layer. It is thus difficult to obtain a sufficient opening ratio, posing a problem of how the efficiency in use of light is to be enhanced. On the other hand, the organic EL display device adopting the top-face luminescence method has such a structure that the opening ratio can be determined regardless of the circuits disposed on the support substrate side. Thus, highly efficient use of light is achieved.
In the planar display device, it is imperative that the light-emission-side electrode disposed on the side of light emission be formed of a light-transmissive conductive film. In the case of the active matrix display device using the top-face luminescence method, it is necessary that a common electrode disposed on the light emission side be formed of a light-transmissive conductive film. It is generally known, however, that a transparent conductive material with light transmissivity has a higher resistivity than ordinary metal materials by two or three orders.
The use of transparent conductive material may lead to non-uniformity in electrode voltage in the screen plane of the light-emission-side electrode, degrading the display quality. This problem becomes more conspicuous as the screen size increases. Incidentally, another problem may arise that the screen size needs to be limited.
As has been stated above, in the prior art, it is difficult to use the active matrix display device using the top-face luminescence method.